its not all about the $$$.
oh wait. apparently it is.
It's about trying to survive in a hostile reimbursement environment. If you had $20,000 would you waste it?
$20,000 in a physician practice could be used on lots of things. Could you buy an US machine and lose the majority of the money?
That's okay, if you value doing US and don't mind taking a 5 figure loss on it. Or you could hire a part time employee to improve efficiency (and help more patients). Or rent more space (and see/help more patients), etc, etc. Or give your staff a bonus/reward for good work, or use it to get on board with an EMR/meaningful use. (But if you already have the machine, use it obviously.)
Is your hospital okay with buying you all kinds of equipment they're going to take loss on? If so, that's great for you I suppose but would also explain why so many hospitals are having to shutter their doors.
In reality, if you're not watching the viability of your department and practice, most likely someone in admin is. If it's a drain for too long, they'll shut you and or your department down at some point most likely, not renew your contract, or bring in a new grad who'll do it for cheaper. In fact, I personally know an employed pain MD, who just had a very substantial portion of his/her practice shut down by the not for profit teaching hospital because they found other ways to "financially utilize" the space, as they would so gently and altruistically describe.
It certainly does suck that it has to be this way, since most of if did choose our careers in Medicine when still young, naive pre-meds.